The present invention relates generally to a printing apparatus, and the invention is more particularly directed to a printer which can print color images clearly without shifting between colors.
Printing apparatuses in which a paper sheet is wrapped about a rotatable platen and a color image printed thereon by a thermal head through a ribbon are well known. An example of such a printer, shown in FIGS. 38 and 39, has a paper ejecting housing 202 and a paper feeding portion 203. The ejecting housing 202 faces toward a printing station 201 and is located at the upper side of a printer 200, while the feeding device 203 is directed to the printing station 201 and is arranged under the ejecting portion. A paper feeding roller 204 is provided above an upwardly opened box-shaped paper feeding tray 207. The feeding tray 207 has a detachable bottom plate 206 for receiving a stack of paper sheets to be printed. When a paper sheet is fed to the platen in order to be printed, as shown in FIG. 38, the bottom plate 206 is lifted up by a lifting mechanism (not shown) so that the reverse surface (i.e., a non-printed) of the top sheet of the stack of paper sheets comes in contact with the peripheral surface of the roller 204 under pressure. When the printed paper sheet is transferred to the paper ejecting housing 202, as shown in FIG. 39, the feeding roller 204 returns to the initial position.
The paper sheet fed to the printing station by the feeding roller 204 is wrapped about a rotatable platen 208 by a pinch roller 209 or so forth. While the platen 208 rotates three cycles, a color image is printed on the paper sheet by a thermal head through a ribbon. When the printing is over, a guide plate 212 comes in contact with the platen 208 so as to separate the printed paper sheet from the peripheral surface thereof. The printed paper sheet is carried out into the ejecting housing 202.
In the above described conventional type paper feeding system, since a feeding roller repeatedly comes in contact with the reverse surface of the uppermost paper sheet within the feeding tray and feeds it to the platen, the agitated contact of the printing surface of the lowermost paper sheet with the bottom of the feeding tray tends to damage it. For the purpose of avoiding damage, is is necessary to provide a protection sheet between the bottom plate and the lowermost paper sheet, this results in inconvenience and relatively high running cost.
Moreover, since new paper sheets are supplied and removed from the top of the stack of sheets within the paper feeding tray, the lowermost paper sheet tends to remain longer.
Further, during printing, the edge of paper sheet wrapped on the platen to collide with the pinch roller, the guide roller or so forth and position of the paper on the platen becomes shifted slightly each revolution which causes the printing start position of each of three colors to be shifted relative to the others.